1. Field of the Invention
The present invention relates to a Chip on Board (COB) package used as a light source and, more particularly, to a COB package which uses a general PCB material such as FR4 for a substrate to significantly reduce the manufacturing costs, increases a heat radiation effect from the light source to improve emission efficiency of the light source, thereby obtaining a high quality light source at low costs.
2. Description of the Related Art
A Chip on Board (COB) package, that uses an LED device as a light source for a backlight unit of a TV or a monitor or a backlight for a mobile phone or a Personal Digital Assistant (PDA), is currently developed.
Such a COB package uses an LED device as a light source and has superior capabilities to a Cold Cathode Fluorescent Lamp (CCFL), but has not been put to practical use due to its price.
The CCFL is prone to environmental pollution with use of mercury gas, slow in response, has low color reproducibility and is unsuitable for miniaturization of an LCD panel.
On the other hand, the LED device is environmentally friendly, capable of high speed response in nanoseconds, effective for video signal stream, capable of impulsive driving, and has color reproducibility of 100%. In addition, the LED device is able to change luminance and color temperature by adjusting the light amounts of red, green, blue LED devices and suitable for miniaturization of an LCD panel. Therefore, the LED device has been actively adopted recently as a light source 110 for a backlight of an LCD panel and the like.
As shown in FIG. 1, a conventional COB package 100 includes LED devices as light sources 110 and a Metal Core Printed Circuit Board (MCPCB) 120 having an insulation layer 122 on which the LED devices are mounted. The light sources 110 and the MCPCB 120 account for a large portion of the costs of the COB package 100.
In order to reduce the price of the COB package 100, reduction of the unit cost of each of the LED devices constituting the light sources 110, reduction of the number of LED devices or change of the material of the MCPCB 120 to reduce the unit cost of the MCPCB 120 can be considered.
FIG. 2 illustrates a stepwise method of manufacturing the conventional COB package 100. To manufacture the conventional COB package 100, first, an MCPCB 120 typically made of Al, with an insulation layer 122 formed on a surface thereof is prepared. Then, a metal pattern 124 of Cu and a dielectric layer 126 are formed on the insulation layer 122, thereby forming electrode pads 128.
Then, a die attachment process is conducted in which the LED devices as the light sources 110 are disposed on the MCPCB 120, followed by a wire bonding process in which the light sources 110 and the electrode pads 128 are electrically connected by wires.
Next, a dome structure 140 is formed using epoxy resin or silicone over each of the light source 110 connected by wires 132, thereby fixing each of the light sources 110 to the MCPCB 120.
Although the conventional COB package 100 easily radiates the heat from the light sources 110 via the MCPCB 120 to the outside and thus thermally effective, its fatal disadvantage is the expensive price due to the MCPCB 120.
In order to overcome such a problem, another conventional COB package 200 has been suggested as shown in FIG. 3, disclosed in Japanese Patent Laid-Open Publication Application No. 2002-335019. The COB package 200 includes a substrate 210 having through holes 212 formed therein and support members 220 of metallic material inserted in the through hole 212. Each of the LED devices 230 is seated in each of the support members 220 and bonded to the pad electrodes 232 by wires 234.
In the COB package 200 with such a structure, the support members 220 are made of metal with good thermal conductivity, through which the heat is transferred from the LED devices 230 to the outside, allowing good heat radiation effects.
However, the conventional package has a complex assembly structure in which each of the support members 220 needs to be fixed into each of the through holes 212 of the substrate 210. In particular, the support members 220 should be prepared respectively for the LED devices 230, incurring high manufacturing costs.